It has become increasingly desirable to improve cooling systems in aerospace applications. Typically, cooling systems provide air conditioning, refrigeration freezer services, electronics cooling, and the like for commercial and other aerospace systems. In general, various known options are available for providing cooling, but such options have drawbacks that limit the design options for aerospace applications.
To accommodate the wide range of possible ambient operating conditions of the aircraft, cooling systems for aerospace applications often use a gas-based system. That is, typical cooling systems include a relatively bulky and low efficiency gas-based system in order to cover the range of conditions that can be experienced during aircraft operation.
To reduce bulk and improve system efficiency, cooling systems have been developed in which a refrigerant is operated over a thermodynamic range between a heat sink temperature that corresponds with ambient conditions of an aircraft, and evaporator temperatures that correspond to cooling devices within the aircraft. For instance, one cooling temperature may correspond to a temperature for providing cooled air to an occupied compartment, while another cooling temperature may correspond to a cooling temperature for providing cooling for electronics. As such and in this example, two evaporating temperatures may be desired to reduce the power required to drive the cooling system.
One known system provides cooling at different evaporator temperatures by providing a two-temperature valve (back pressure regulator) in a suction line that keeps low-side pressure refrigerant liquid, and vapor in one evaporator is at a higher pressure than in another evaporator. A check valve is located in the suction line coming from the colder (i.e., lower pressure) evaporator to prevent refrigerant back flow. However, if the evaporating pressures are significantly different from one another in the two evaporators, back pressure regulators (which are isenthalpic expansion devices) are typically installed downstream of each evaporator, which can lead to throttling losses that can be significant, resulting in thermodynamic loss and reduction of cooling performance.
Thus, there is a need to improve cooling in aircraft.